1. Field of the Invention
The invention relates to a wobble drive for a structural part moving in translation and being maintained relative to a stationary structural part in a predetermined angular relationship, said drive consisting essentially of a wobble rod:
moved by means of a crank drive mechanism and seated for the purpose at its end on the crank side with a first spherical section in a bearing bush of the crank,
supported at its other end with a second spherical section in a bearing bush of the stationary structural part, coaxially relative to the crank mechanism,
and comprising a third spherical section between its two ends, supported rotatingly and pivotingly in a bearing bush in the hub of the translationally moving structural part.
Wobble drive mechanisms of this type are especially suitable for devices, such as rotating piston positive displacement machines.
2. Discussion of Related Art
Wobble drives of the aforementioned type are known, for example from DE 2 603 462 and U.S. Pat. No. 3,560,119. All of those disclosed installations are displacement machines for compressible media. They each comprise a working chamber defined by helical circumferential walls extending vertically from a side wall and leading from an inlet located outside the helices to an outlet inside the helices. They further contain a helical displacement body extending into the working chamber. The latter is supported rotatingly without rotation relative to the working chamber. Its center is eccentrically offset relative to the center of the circumferential walls, so that the displacement body is always in contact with both the outer and the inner circumferential walls of the working chamber along at least one advancing line.
During the operation of the machine therefore a plurality of sickle shaped working spaces are enclosed. The working spaces move from the inlet to the outlet through the working chamber. Depending on the angle of contact of the helix, the volume of the working medium conveyed may be gradually reduced with a corresponding increase of the pressure of said medium.
In those known machines, a tumble drive is always the means to convert the rotating motion of the driving machine into the translatory motion of the displacer. Its radial offset is limited by the contact of the helical ribs with the walls of the working chambers. This limitation theoretically corresponds to a circle, in this case a translational circle.
The drive solution in DE 2,603,462 consists of an eccentric body mounted with a counter weight on the drive shaft, upon which a drive disk is located by means of a ball bearing. The latter is equipped with four ball jointed sockets in which the ball end of a wobble rod is located. The balls there are only in line contact with their sockets. During a rotating motion of the drive shaft, the rotor body is placed into a circling but not rotating motion by the wobble rods. In addition to the driving function, in this solution the wobble rods also secure the body against rotation.
In the configuration according to U.S. Pat. No. 3,560,119, the pivot of the wobble rod on the drive side is supported rotatingly and pivotingly in an eccentric position by means of a pendulum ball bearing. To prevent the rotation of the displacer itself, the second and third ball sections are provided with sectional crowns, for example, teeth, which engage the correspondingly profiled counter pieces in the displacer and the stationary housing part and are pivotingly supported in them. The wobble shaft is axially secured by means of a retaining disk fitting into the stationary housing part.
In the known machines, the relative rotating motion is always transmitted by a highly stressed and thus expensive ball bearing. Furthermore, no measure is provided to insure the operation without clearance of the machine in case of the wear of the material of the wobble rod or rods.